1. Field of the Invention
Embodiments of the invention generally relate to waste abatement apparatuses and methods for processing a waste solution after a plating process, and more specifically, a waste solution containing metal ions and reducing agents after an electroless deposition process or an electrochemical deposition process.
2. Description of the Related Art
The copper damascene process is widely established and has brought higher performance to semiconductor devices. Copper materials may be deposited by an electroless deposition (e-less) process or an electrochemical plating (ECP) process. Copper has replaced aluminum because of its lower resistivity and higher reliability. However, copper still suffers from electromigration and stress migration reliability issues as geometries continue to shrink, and current densities increase. Engineers have successfully solved these reliability problems by depositing a capping layer (e.g., cobalt tungsten phosphide (CoWP)) over the copper surface during a selective e-less process. A capping layer of CoWP deposited by an e-less process is self-aligned to copper and forms a smooth conformal film.
Generally, a chemical plating solution (e.g., e-less or ECP) contains a metal-containing compound, a reducing agent, a complexing/chelating agent, a pH adjusting agent, and other additives. A copper plating solution may contain copper sulfate as the metal-containing compound, glyoxylic acid as the reducing agent, ethylenediamine tetraacetic acid (EDTA) as the complexing/chelating agent, and tetramethylammonium hydroxide (TMAH) as the pH adjusting agent, and 2,2′-dipyridine or polyethylene glycol as an additive. A cobalt plating solution usually contains several metal-containing compounds, as well as several reducing agents. For example, an e-less plating solution for depositing CoWP usually contains a cobalt source, a tungsten source, a hypophosphite source, probably a boron-containing reducing agent, such as dimethylamine borane (DMAB). Although copper, cobalt, or tungsten-containing plating solutions are prevalent in the art, other metal-containing plating solutions are common for depositing nickel, platinum, palladium, molybdenum, tin, chromium, silver, gold, or alloys thereof.
Upon completion of a plating process, the used or depleted chemical plating solution is usually disposed of as a waste solution. Metal ion contaminants (e.g., cobalt, tungsten, nickel, or copper), reducing agents, and complexing/chelating agents are dissolved in the waste solution and pose a challenge for waste abatement processes.
Some references have proposed processes to reuse or regenerate depleted plating solutions by supplementing the depleted chemical components, such as metal salts or reducing agents. Several references have disclosed processes to reduce the concentration of copper ions or other metal ions from within used polishing solutions, such as CMP slurries. However, depleted polishing solutions generally do not contain reducing agents that are readily found in plating solutions, especially e-less solutions. The reducing agents contained within waste solutions need to be removed or destroyed during waste abatement processes. Often, waste solutions containing reducing agents are dangerous to handle due to hydrogen gas evolution formed by the reducing agents. The lower explosion limit (LEL) of hydrogen gas in the ambient air is about 3.8 molar percent (mol %).
Therefore, there is a need for a method and an apparatus to remove metal ions and reducing agents from waste solutions derived of depleted plating solutions while reducing processing complexity and improving safety, processing efficiency, and throughput during waste abatement.